This invention relates to drive axle assembly, and more particularly to an inverted portal drive axle assembly with an external shaft for driving a mass transit vehicle where the drive axle assembly provides a significantly lower floor profile.
Mass transit vehicles, such as trolley cars, buses, and the like typically have seats aligned at the lateral sides of the vehicle, with a central aisle and floor extending along the vehicle. In order to facilitate entering and exiting from the vehicle, it is desirable to have the vehicle floor and aisle positioned relatively low to the ground. This provides faster cycle time during stops and facilitates boarding for all passengers, especially for elderly and disabled passengers, as well as for children.
Mass transit vehicles typically have several axles that support, drive and steer the vehicle. Many such vehicles provide a rigid axle having an input positioned off-center near one wheel end to form an inverted portal axle configuration. This configuration permits the vehicle floor to be positioned closer to ground level than would occur with a traditional drive axle configuration, i.e., a non-inverted portal axle configuration. However, there still is a need to move the vehicle floor even closer to the ground.
A traditional inverted portal axle configuration has a short axle shaft that drives one wheel assembly and a long axle shaft that drives the opposite wheel assembly. The axle shafts have different lengths due to the input being positioned off-center, i.e., the input is positioned closer to one wheel assembly than the other wheel assembly. The axle shafts are enclosed within an axle housing that extends between the wheel assemblies and underneath the vehicle floor.
One disadvantage with the inverted portal axle configuration is that the low floor profile is limited by the portal axle housing. There is a minimum required clearance distance between the vehicle floor and the axle housing. There is also a minimum required clearance distance between the axle housing and the axle shaft. Currently, the height between the vehicle floor and ground level is limited by sum of these two (2) minimum required clearance distances plus the wall thickness of the housing.
Accordingly, it is desirable to provide an inverted portal axle configuration that provides an improved low floor profile to facilitate access to the vehicle as well as overcoming the other above-mentioned deficiencies with the prior art.